The invention relates to an apparatus for aerobic biological cleaning of waste water with a tank for holding the waste water and a wheel that can rotate in the tank around a horizontal axis, whereby the wheel has a number of chambers that are arranged axially in succession about the circumference of the wheel. Each chamber is provided with an opening, which adjacent the top dead center position of the wheel, emerges out of the waste water and is pointed upward, and adjacent the bottom dead center position of the wheel is submerged into the waste water and is pointed downward.
Apparatuses of this type for aerobic biological cleaning of waste water according to the so-called combined immersion element-activated sludge process are known in many variations from the state of the art.
In such device, the waste water cleaning occurs, on one hand, by the free-floating activated sludge (suspended biomass) and on the other, by adhering microorganisms on growing surfaces of the rotating immersion element formed by the walls of the chambers (sessile biomass). In this way, the activated sludge process is combined in one unit with the immersion element process.
Bucket wheels and tube wheels are used as preferred construction shapes for the combined process.
The bucket wheel with bucket segments is composed of several plastic segments arranged parallel to the axis. These consist of a number of profiled polypropylene plates. Their distinguishing characteristic is the forming of chambers (bucket segments), which are used for the entry of air during submerging the chambers in the waste water and enlargement of the colonization surfaces. They ensure the oxygen supply according to the requirements.
The tube wheel is identical in function to the bucket wheel. However, the colonizing surface and the volume of the air chambers are smaller. The modified construction shape results from the specific goals of the particular application. The tubes are arranged on the periphery of the wheel parallel to the axis of the wheel. They are typically constructed of joined plastic disks.
Equipping the rotating wheel with a paddle is generally known. This is used for mixing the waste water when the wheel turns in the tank.
The bucket wheel and/or tube wheel is driven by means of an electric motor by way of a gear that acts on the central bearing shaft of the wheel.
An apparatus of the type named at the beginning with the use of a tube wheel is known from DE 25 44 177 C2 and DE-OS 26 38 665. One apparatus that uses a bucket wheel is described in DE 34 11 865 C2 and EP 0 881 990 B1. Reference is made to EP 1 338 566 A1 regarding the further state of the art.
What is disadvantageous in the known apparatuses is the very great amount of construction effort needed in connection with the drive, which is necessary due to the electric motor and its mounting and the interaction of electric motor and gear, as well as gear and wheel. Besides that, this means a great deal of maintenance effort for the wheel drive. It is also disadvantageous that only the air that is pressed into the waste water by means of the chambers under the water surface during submersion of the chambers into the waste water contributes to the cleaning process of the waste water, whereby this air already escapes out of the chamber and goes back to the water surface when the chamber moves beyond bottom dead center.
According to the state of the art, forming the wheel of a number of disk or honeycomb elements arranged at a distance from each other that do not form any chamber and do not form any enclosed spaces apart from the openings is already known. To this extent, no compression of the air can occur with such a honeycomb immersion element.
U.S. Pat. No. 5,755,961 describes an aquarium system with an apparatus for pumping water through the system and for supporting bacterial grown. In this case, a treatment unit has a tank for water and a device for movement of the water. This device is designed as a wheel that is provided on its circumference with air capturing means. Below the wheel, in the area of the air capturing elements submerged in the water, an outlet opening of an air pipe is placed so that the rising air that is output from it enters into the air capturing means and as a result the wheel is turned. The wheel has a first hollow section and a second section, which is used to displace the water and has a biological filter for promoting the bacterial growth. When the wheel turns, the second section of the wheel submerges into the water and causes an increase of the water level in the tank. As a result of this, the water can leave the tank over an overflow threshold. As soon as the second section has emerged from the water again, the lower water level develops in the tank again, with the consequence that water flows out of the system into the tank. With continued rotation of the wheel, a pumping of the water through the system thus occurs. When the second section emerges out of the water, about half the wheel submerges into the water located in the tank.
U.S. Pat. No. 3,886,074 describes an apparatus for biological treatment of waste water, wherein wheel-shaped immersion element submerges with less than half of its diameter into waste water located in a tank and is rotated around a horizontal axis by means of air. The air is output below the immersion element, behind its bottom dead center, from an air pipe and enters into pocket-shaped parts that are arranged on the circumference of the wheel.
U.S. Pat. No. 4,668,387 describes a device for treating waste water that also has an immersion element that can rotate around a horizontal axis in a tank filled with waste water. It is suggested that the immersion element submerges completely into the waste water and is driven by means of compressed air that is supplied in a lower area of the tank that holds the immersion element.
EP-A 14 453 discloses an immersion trickling filter with chambers to which a gas containing oxygen is supplied so the immersion trickling filter is turned.